From BBC News today, Monday:
"Germany, Belgium, Croatia and Switzerland are fully reopening borders with EU countries on Monday.
Travellers from the UK will be able to visit these four countries without quarantine or restrictions upon arrival, though they still face quarantine on return to the UK."
So, if you can get a ferry to Ostend, you can have a travelling holiday around three countries, with the disadvantage of having to quarantine at home for a fortnight afterwards. If the trip is long enough, the rules about quarantine may have changed by the time you get back.